Recently, optical disk drives such as audio compact disk (CD) and the like are actively used increasingly in the range of applications and improved in performance. Compact Disc-Read Only Memory (CD-ROM) and Digital Versatile Disc-Read Only Memory (DVD-ROM) have been already put into practical use. The market of optical disk drive capable of recording on CD-R media and CD-RW media has been rapidly expanding in recent years.
In optical disk drive capable of recording on the CD-R media and CD-RW media, the recording condition of an optimum LD power is determined through trial writing which is generally executed in a trial-writing area (Power Calibration Area: PCA) previously provided on the media. Under the recording condition obtained from the result of the trial writing, data is recorded in a data area of the optical disk. A method of obtaining the optimum LD power through the trial writing in the PCA is called Optimum Power Control (OPC). The principle of the OPC will be described below with reference to the drawing.
FIG. 7 shows the relationship between the LD power for recording on the optical disk in a conventional optical disk drive, and an asymmetry value and amplitude of a read signal.
In FIG. 7, the horizontal axis represents the LD power for recording on the CD-R media and CD-RW media, and the vertical axis represents the asymmetry value of the read signal read out of the CD-R media and the amplitude of the read signal read out of the CD-RW media. Also, a plot H shows the relationship between the LD power for recording on the CD-R media, write-once media, and the asymmetry value of a read signal. A plot I shows the relationship between the LD power for recording on the CD-RW media, re-writable media, and the amplitude of read signal.
As shown in FIG. 7, in the CD-R media, according to an increase of the LD power for data recording, the asymmetry value of the read signal read out of the data decreases. In CD-RW media, according to an increase of the LD power for data recording, the amplitude of the read signal read out of the data increases. This indicates that the LD power for recording on the CD-R media correlates a lot with the symmetry value of the read signal, and that the LD power for recording on the CD-RW media correlates a lot with the amplitude of the read signal.
The conventional optical disk drive with such characteristics previously stores the asymmetry value or amplitude of the read signal as a target performance, and switch the LD power in multiple stages in the PCA of the optical disk in order to record OPC test data. Then the drive reads the OPC test data recorded at each LD power for each multiple stage. The drive executes the OPC through controlling the LD power so that the asymmetry value of the read signal detected by an asymmetry value detector for the write-once CD-R media may be consistent with the stored target performance, and that the amplitude of the read signal detected by an amplitude detector for the re-writable CD-RW media may be consistent with the target performance.
The PCA and a method for the OPC described above are prescribed in the Compact Disc Recordable Standards (Orange Book Standards) of Phillips Co. and Sony Corporation.
In the Orange Book standards, a single optical disk has up to 99 recordable tracks. Correspondingly to this, the optical disk has the PCA for maximum 100 times recording exceeding the maximum number of tracks. Thus, the OPC can be executed maximum 100 times according to the standards.
FIG. 8 is the configuration diagram of the PCA mentioned in the Orange Book standards. The optical disk includes a PCA 26, the area for executing the OPC. The PCA 26 is divided into a test area 27 for recording the test data corresponding to the changed LD power in multiple stages, and a count area 28 indicating the number of tests.
The PCA 26 is allotted with an area for 100 times tests on the optical disk, and a single-trial write area 27 includes 15 absolute time in pre-groove (ATIP) frames, and a count area 28 for a single-trial includes a single ATIP frame.
A recording speed of the recordable optical disk drive has increased year after year, the optimum LD power is required to increase for recording on the optical disk. The relationship between the recording speed and optimum LD power for recording will be described below.
FIG. 9 shows the relationship between the recording speed onto the write-once CD-R media and the LD power required for recording in the conventional optical disk drive. In FIG. 9, the horizontal axis represents the recording speed of the optical disk drive, and the vertical axis represents the LD power required for achieving the recording speed.
As shown in FIG. 9, in the write-once CD-R media, the required LD power is 15 mW for a fourfold speed, while the power is 21 mW for an eightfold speed, and is 26 mW for a 12-fold speef. Further, for a 16-fold speed in the future, the required LD power is about 30 mW. The LD power is the value of laser light emitted from an object lens toward the optical disk. The optical path from the semiconductor laser to the object lens exhibits a loss at approximately 30% place due to optical components such as collimator lens and riser lens. Therefore, the LD power emitted from the semiconductor laser is generally required to be about 3.33 times the LD power emitted from the object lens, that is, the required LD power output is about 100 mW for the recording at the 16-fold speed. And a high-output semiconductor laser is accordingly needed.
The LD power required for recording is affected by a focus offset of the object lens. Alteration of the LD power required for recording in relation to the focus offset will be described below. The focus offset is expressed by a value relative to an amplitude of a focus error signal detected by a focus error signal detector.
FIG. 10 shows the relationship between the focus offset of object lens and the LD power in the write-once CD-R media. In FIG. 10, a recording is executed at a eightfold speed while maintaining the asymmetry value of the read signal in constant. FIG. 10 also shows the relationship between the focus offset of object lens and the LD power for the write-once CD-R media for each of five conventional optical disk drives, where the same mark corresponds with the same optical disk drive.
In FIG. 10, the horizontal axis represents the focus offset. The offset being zero indicates in-focus, the offset being positive indicates that the object lens is too close to the optical disk, and the offset being negative indicates that the object lens is apart from the optical disk. The vertical axis represents the LD power at which the asymmetry value after the recording of the write-once CD-R media is maintained in constant. The constant asymmetry value of the read signal after recording indicates that a pit formed on the optical disk has a constant length. The low recording power with which the asymmetry value after recording of the write-once CD-R media becomes constant indicates that the power required for recording can be reduced. A recording accuracy can be improved through making the asymmetry value nearly zero.
As shown in FIG. 10, when the focus offset is zero, the LD power required for recording is not always at the lowest value. This is caused by astigmatism generated in the semiconductor laser and the object lens. The astigmatism makes a laser spot collected through the object lens has respective different shapes on the optical disk and a photo sensor for detecting a reflected light of the laser. The laser output, upon being capable of reaching enough maximum power, solves such problem of focal deflection through increasing for the recording. Even if the spot shape of laser light on the optical disk is expanded due to the focal deflection, and even if the pit is not formed accurately, the drive increases the LD power to reduce the lowering of recording accuracy.
However, a high-speed optical disk drive based on the conventional system requires a high-output semiconductor laser. Such conventional drive has a problem such that increasing the LD power in order to make the asymmetry value of the read signal nearly zero to improve the recording accuracy shortens the life time of the semiconductor laser or increases a consumed current in the optical disk drive due to an increased current of driving the semiconductor laser.